[Haskell-cafe] Restricted type classes

David Menendez dave at zednenem.com
Mon Sep 6 23:22:55 EDT 2010

On Mon, Sep 6, 2010 at 10:22 PM, wren ng thornton <wren at freegeek.org> wrote:
> On 9/6/10 1:33 PM, David Menendez wrote:
>> For that matter, can you even describe what pure is intended to do
>> without reference to<*>  or join?
> As already stated: fmap f . pure = pure . f

That's pretty general. For lists, the functions having that property
include const [], \x -> [x,x], and repeat.

In fact, I think *every* appropriately-typed function satisfies that
law. Does anyone know of a counter-example?

Dave Menendez <dave at zednenem.com>

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